Unbalancer 9-pin.pdf - Tube CAD Journal

18Unbalancer 9-Pin PCBTransformer-Rectifier ConfigurationsTransformers As shown below, the Unbalancer high-voltage power supply can useeither a conventional tube-intended, high-voltage, center-tapped transformer or anon-center-tapped power transformer. The topmost transformer’s current rating is inrectified DC yield, while the bottommost transformer, in AC current yield;nonetheless, both transformers deliver the same amount of power for the powersupply. Never overlook that the rectifiers in the center-tap arrangement will see twicethe peak reverse voltage that the rectifiers see in the full-wave bridge arrangement.R17D2R14C8C7R13D1 J9ACCTACCenter-TappedTransformer480Vct @ 130mAR17D1R13C8D2R14ACC7Non-Center-TappedTransformerD3R15J9ACD4R16240Vct @180mAStep-up power transformers (115V to 230V), either standard EI or toroidal core,are excellent choices for the B+ transformer, as 230Vac becomes about 325Vdc to340Vdc rectified, depending on the transformer’s regulation, the current drawn bythe load, and the wall voltage. (Of course, if you live in a country that uses 230V wallvoltage, then the transformer will not be a step-up but a an isolation transformer.)One danger is over voltage, as the power supply capacitors are only rated400Vdc (or 200V) and the solid-state rectifiers do not drop the 10V to 40V that a tuberectifier would. In other words, be careful not to fry the capacitors with too muchvoltage. Furthermore, many high voltage power transformers suffer from poorregulation, which is the measure of the transformer’s secondary voltage with no loadover the secondary voltage with a load. For example, a 100Vac power transformerwith a regulator figure of 10% will put out 110Vac with no load and 100Vac with itsrated load. By the way, a regulation figure of 10% is fairly impressive in a highvoltagetransformer, as many present 20% or 30% figures. Unfortunately for thepower supply capacitors, tubes are slow to conduct, requiring time to warm up first.Thus during startup, the power transformer will effectively see no load, so itssecondary voltage will equal its rated value plus its regulation figure againstsecondary voltage: Vpeak = 1.414 x (1 + Regulation) x Vsec. Be warned.